







































 
 

 

12 
© 2025 by the author; licensee Asian Online Journal Publishing Group 
 

Agriculture and Food Sciences Research 
Vol. 12, No. 1, 12-18, 2025 

ISSN(E) 2411-6653/ ISSN(P) 2518-0193 
DOI: 10.20448/aesr.v12i1.6554 

© 2025 by the author; licensee Asian Online Journal Publishing Group 

 
 

 

 
 
 
Sustainable biomass sourcing through agroforestry systems based on poplar and 
eucalyptus as fast-growing trees 

 
Niels Thevs   

 

 
 
Independent Researcher, Gluckstrasse 2, 53115 Bonn, Germany. 
Email: niels.thevs@giz.de  

 
Abstract 

Global biomass demand is expected to increase during the next decades, which bears risks of 
accelerating food insecurity and biodiversity loss. Therefore, guidelines and standards have been 
developed to ensure sustainable biomass sourcing as feedstock for material or energetic purposes. 
This review addresses the question of how fast-growing trees in agroforestry systems increase 
biomass production and serve as sustainably sourced biomass feedstock. The Land Equivalency 
Ratio (LER), a measure of productivity gains by agroforestry, was positively correlated with the 
number of trees per hectare (R = 0.561) and with the spacing between tree rows (R = 0.26). The 
former corresponds to a high wood yield of the given agroforestry systems, while the latter 
corresponds to high crop yields within the agroforestry systems. The LER of tree windbreak 
systems (spacing between tree rows >100 m) was 1.1-2.1. Tree windbreak systems adhered to 
principles of sustainable biomass sourcing, while other agroforestry systems often provided lower 
food crop yields compared to the corresponding crop monoculture. Still, such agroforestry systems 
help to diversify incomes, have the potential to protect croplands against erosion, and improve the 
microclimate. Depending on local conditions, biomass from those agroforestry systems can be 
considered sustainable, too. 

 
Keywords: Alley cropping, Bioeconomy, Biomass demand, Land equivalency ratio, Material use, Tree windbreak systems, Woody 
biomass. 

 
Citation | Thevs, N. (2025). Sustainable biomass sourcing through 
agroforestry systems based on poplar and eucalyptus as fast-growing 
trees. Agriculture and Food Sciences Research, 12(1), 12–18. 
10.20448/aesr.v12i1.6554 
History:  
Received: 19 February 2025 
Revised: 24 March 2025 
Accepted: 28 March 2025 
Published: 4 April 2025 
Licensed: This work is licensed under a Creative Commons 

Attribution 4.0 License  
Publisher:  Asian Online Journal Publishing Group 

Funding:  This study received no specific financial support.    
Institutional Review Board Statement: Not applicable. 
Transparency: The author confirms that the manuscript is an honest, accurate, 
and transparent account of the study; that no vital features of the study have 
been omitted; and that any discrepancies from the study as planned have been 
explained. This study followed all ethical practices during writing. 
Competing Interests: The author declares that there are no conflicts of 
interests regarding the publication of this paper. 
 

 

Contents 
1. Introduction ...................................................................................................................................................................................... 13 
2. Methods ............................................................................................................................................................................................. 13 
3. Results ................................................................................................................................................................................................ 14 
4. Discussion .......................................................................................................................................................................................... 15 
5. Conclusion ......................................................................................................................................................................................... 17 
References .............................................................................................................................................................................................. 17 
 

 

 

 

 

 

 

mailto:niels.thevs@giz.de
https://creativecommons.org/licenses/by/4.0/
https://creativecommons.org/licenses/by/4.0/
https://www.doi.org/10.20448/aesr.v12i1.6554
https://orcid.org/0000-0003-1923-4280


Agriculture and Food Sciences Research, 2025, 12(1): 12-18 

13 
© 2025 by the author; licensee Asian Online Journal Publishing Group 

 

 

Contribution of this paper to the literature:  
This study, for the first time, pools together data on wood and crop yields of agroforestry systems with 
fast-growing trees. These data are discussed to assess agroforestry systems as biomass feedstock in light 
of the emerging issue of sustainable biomass sourcing for the bio-economy. 

 
1. Introduction 

Global biomass demand is expected to increase during the next decades, as shown by, for instance, [1], who 
assumed that the global biomass demand will increase from 12.14 Gt in 2011 to between 17.13 Gt and 20.36 Gt by 
2050, in order to satisfy the needs for increased food production as well as for the material and energetic use of 
biomass. Biomass is primarily used to feed livestock (58% of global biomass use), bioenergy (amounting to 16%), food 
(14%), material use (10%), and biofuels (biodiesel and bioethanol for transport account for 1%) [1].  

In the course of reducing the use of fossil carbon sources for material uses, it is claimed that the overall 
consumption of materials needs to be reduced, recycling needs to be increased, and bio-based products need to be 
used for the amount of production of virgin materials (such as chemicals, but also construction materials) that cannot 
be covered by the reduction of consumption and recycling [2]. This is underlined by UNEP [3], which states that 
a sustainable and circular bioeconomy must be based on prioritizing the use of biomass to maximize well-being, while 
the conversion of biodiversity- and carbon-rich natural systems must be avoided. 

Yet, the production and sourcing of an increasing amount of biomass for human demands bear high risks of 
accelerating food insecurity, biodiversity loss, and climate change. Therefore, guidelines, safeguards, and standards 
have been developed to ensure sustainable biomass sourcing as feedstock for material or energetic purposes across 
different feedstocks [4, 5], as well as for specific feedstocks, such as sugar cane [6], soy [7], or palm oil [8]. To 
address the concerns regarding food insecurity, biodiversity loss, and climate change, the BFA [4], for instance, 
stipulated the following principles that sustainably sourced biomass must fulfill: i) it is derived from renewable 
biomass whose production is sustainably managed, ii) it does not adversely impact food security and affordability and 
maintains or improves social and economic conditions along with ecosystem services in producing communities, iii) 
it does not directly or indirectly result in the destruction of critical ecosystems or loss of high conservation value 
habitats, and iv) it contributes to landscape resilience and is resilient to the impacts of climate change. Other 
standards, such as RSB [5], adhere to very similar principles. 

Agroforestry (AF) systems, which according to FAO [9] deliberately integrate woody perennials (trees, shrubs, 
palms, bamboos, etc.) with agricultural crops and/or animals, are acknowledged to increase overall biomass 
productivity compared to respective monocultures of trees and crops, while providing a number of benefits to improve 
food insecurity, contribute to halting biodiversity loss, and help mitigate and adapt to climate change. Furthermore, 
AF has the potential to improve soil fertility, reduce erosion, improve water quality, sequester carbon, increase 
aesthetics [10], and enhance the microclimate for crops [11].  

In particular, fast-growing trees can contribute substantially to increasing the productivity of AF systems. 
Hence, in the first step, this paper assesses the productivity gains of AF systems from fast-growing trees, followed 
by a discussion of how far the criteria for sustainable biomass sourcing are met. Thereby, this paper focuses on AF 
systems with the two fast-growing tree species, poplar and eucalyptus, which are listed among the most widely used 
fast-growing tree species in AF globally [12]. In this paper, the jurisdictional and societal principles are not studied, 
such as sustainably sourced biomass must adhere to labor laws and must economically benefit local and rural 
communities. 

The Land Equivalency Ratio (LER) after [13] is a widely used metric to express productivity gains of 
agroforestry (AF) systems versus corresponding monocultures of crops and trees. The LER is calculated as follows. 

𝐿𝐸𝑅 =
𝑌𝑖𝑒𝑙𝑑 𝑡𝑟𝑒𝑒 𝑎𝑔𝑟𝑜𝑓𝑜𝑟𝑒𝑠𝑡𝑟𝑦

𝑌𝑖𝑒𝑙𝑑 𝑡𝑟𝑒𝑒 𝑟𝑒𝑓𝑒𝑟𝑒𝑛𝑐𝑒 
+

𝑌𝑖𝑒𝑙𝑑 𝑐𝑟𝑜𝑝 𝑖𝑛 𝑎𝑔𝑟𝑜𝑓𝑜𝑟𝑒𝑠𝑡𝑟𝑦

𝑌𝑖𝑒𝑙𝑑 𝑐𝑟𝑜𝑝 𝑟𝑒𝑓𝑒𝑟𝑒𝑛𝑐𝑒
 

Yield tree reference is a plantation of the given tree, while yield crop reference refers to a field plot of the given 
crop with no kind of intercropping. Thus, LER only considers biomass yield changes (wood yields from the trees and 
crop yields), regardless of their economic value or further benefits beyond sheer biomass. Crop-related LER (LERc) 
after [14] focuses on crop yield changes by AF systems and therefore highlights the benefits associated with crops 
rather than trees. Hence, LERc captures the impact of AF systems on food supply. 

𝐿𝐸𝑅𝑐 =  
𝑌𝑖𝑒𝑙𝑑 𝑐𝑟𝑜𝑝 𝑖𝑛 𝑎𝑔𝑟𝑜𝑓𝑜𝑟𝑒𝑠𝑡𝑟𝑦 − 𝑌𝑖𝑒𝑙𝑑 𝑐𝑟𝑜𝑝 𝑟𝑒𝑓𝑒𝑟𝑒𝑛𝑐𝑒

𝑌𝑖𝑒𝑙𝑑 𝑐𝑟𝑜𝑝 𝑟𝑒𝑓𝑒𝑟𝑒𝑛𝑐𝑒
 

 

2. Methods 
The productivity gains by agroforestry (AF) of fast-growing trees were assessed through a literature review 

using the search terms "land equivalency ratio" AND "poplar" and "poplar agroforestry" as well as "land equivalency 
ratio" AND "eucalyptus" and "eucalyptus agroforestry," which were used in Google Scholar and Web of Science. 
Papers were screened for absolute crop yield data for crops within AF in comparison to the same crop grown as a 
monoculture to be able to calculate LERc. Those papers that, in addition to crop yield data, contained tree yield data 
for the AF trees and trees from plantations were used to calculate LER values. 

Crop yields and tree yields were converted into t ha-1 yr-1. Thereby, tree yields referred to above ground woody 
biomass, mostly stem wood biomass, which was divided by the given tree age. Part of the studies on poplar-based 
AF systems reported tree or stem volumes, which were converted into biomass with a wood density of 0.35 t m-3 
after [15].  

Next to the crop and tree yield data, the following data were extracted from the selected papers, as far as they 
were available. 

• Site data: Geographical location (by name), climate classification (Köppen-Geiger), mean air temperature, and 
annual precipitation. 

• AF system data: Type of AF system, tree species (clone, if available), spacing between tree rows and within 
rows, number of trees per hectare, tree height, and crop. 



Agriculture and Food Sciences Research, 2025, 12(1): 12-18 

14 
© 2025 by the author; licensee Asian Online Journal Publishing Group 

 

 

LER and LERc values were grouped by tree (poplar and eucalyptus), AF system, and crop in order to calculate 

the respective averages and standard deviations. The differences between averages were tested for significance at α 
< 0.05 through a t-test (the averages by tree) and by an analysis of variance, respectively. 

The studies of the AF experiments reviewed did not contain tree windbreaks or field boundaries of wide spacing 
(100 m and more), so this gap was closed with crop yield data from [16] and our own tree yield data. Those own 
tree yield data stem from a dataset of poplar-based (P. nigra, local clone Mirza Terek) tree windbreaks in Kyrgyzstan, 
Jalalabad Region, (spacing of 200 m) and plantations from the same poplar clone in that region. The selected tree 
windbreaks and plantations consisted of 10-year-old trees. 

 

3. Results 
A total of 23 field experiments were screened for this study, which yielded a total of 100 LER datapoints, of 

which 58 and 42 datapoints were from poplar and eucalyptus AF systems, respectively. The vast majority (87%) of 
those datapoints stemmed from experiments that were laid out as alley cropping systems or contiguous plantations 
with the given crop as understory vegetation, while only 13% were oriented around tree rows as field boundaries. 
The tree spacing within the contiguous plantations was 3m x 3m, while most of the alley cropping had spacings 
between tree rows of less than 8 m. The majority of all datapoints (70%) stemmed from AF systems with trees aged 
5 years and younger. Nine additional datapoints allowed for the calculation of LERc only, because no tree data were 
reported. These nine additional datapoints stem from experiments laid out as alley cropping, with eight datapoints 
from poplar AF systems and one from a eucalyptus AF system. 

The LER and LERc averaged across all data points were 1.51 and -0.29, respectively. The LERs divided by AF 
tree species were 1.57 for poplar and 1.42 for eucalyptus AF systems, whereby the two did not show significant 
differences (Table 1). The LERs divided by AF system did not differ significantly either (Table 2). Additionally, LER 
by major crops did not show significant differences (Table 3). Out of the 100 data points, only six show an LER < 1; 
these six data points all stem from eucalyptus AF systems, while the minimum LER among the poplar AF systems 
was 1.14 (Table 1). 
 
Table 1. Land equivalency ratio (LER) of AF systems by poplar and eucalyptus. 

Tree LER average ± standard 
deviation 

LER maximum LER minimum Number of data points 

Poplar 1.57 ± 0.37 2.78 1.14 58 
Eucalyptus 1.42 ± 0.4 2.19 0.68 42 
All data points 1.51 ± 0.39 2.78 0.68 100 

 
Table 2. Land equivalency ratio (LER) of the different AF systems: alley cropping, contiguous plantations with the given crop as understory 
vegetation, and tree rows as field boundary. 

Tree LER average ± standard deviation LER maximum LER minimum Number of data points 

Alley cropping 1.48 ± 0.36 0.68 2.78 81 
Contiguous 
plantations 

1.56 ± 0.19 1.27 1.83 6 

Field boundary 1.62 ± 0.57 0.85 2.23 13 

 
Table 3. Land equivalency ratio (LER) of AF systems by crops, poplar and eucalyptus pooled together under each crop. 

Crop LER average ± standard 
deviation 

LER maximum LER minimum Number of data 
points 

Wheat 1.51 ± 0.47 2.78 0.85 35 
Switchgrass 
(Panicum virgatum 
L.) 

1.46 ± 0.18 1.71 1.26 6 

Sorghum 1.55 ± 0.24 2.01 1.18 24 
Fodder grass 1.76 ± 0.19 1.94 1.45 5 
Cowpea 1.5 ± 0.16 1.64 1.23 5 
Barley 1.58 ± 0.66 2.77 1.22 5 

 
The LERc values of poplar and eucalyptus agroforestry (AF) systems did not differ significantly (Table 4). 

Divided by AF system, the LERc of field boundary AF systems was significantly higher than the LERc values of 
alley cropping and plantation with crops as understory vegetation (Table 5).  

 
Table 4. Crop related land equivalency ratio (LERc) of AF systems by poplar and eucalyptus. 

Tree LERc average ± standard 
deviation 

LERc maximum LERc 
minimum 

Number of data points 

Poplar -0.23 ± 0.23 0.35 -0.74 66 
Eucalyptus -0.37 ± 0.24 0 -0.82 43 
All data points -0.29 ± 0.24 0.35 -0.82 109 

 
Table 5. Crop related land equivalency ratio (LERc) of the different AF systems: Alley cropping, contiguous plantations with the given crop 
as understory vegetation, and tree rows as field boundary.  

Tree LERc average ± standard 
deviation 

LERc maximum LERc minimum Number of data 
points 

Alley cropping -0.3 ± 0.24a 0.35 -0.82 89 
Contiguous 
plantations 

-0.48 ± 0.21a -0.17 -0.73 7 

Field boundary -0.08 ± 0.13b 0.14 -0.25 13 
Note: The letters a and b indicate significant differences of the averages of LERc (α = 0.05). 



Agriculture and Food Sciences Research, 2025, 12(1): 12-18 

15 
© 2025 by the author; licensee Asian Online Journal Publishing Group 

 

 

The large majority of the LER datapoints (94%) and all nine additional LERc datapoints showed lower crop 
yields inside the AF system compared to the corresponding monoculture crop yields. This crop yield reduction 
increased with tree age and thus tree height (see data points by Kimura et al. [17]). Among the experiments listed 
here, crop yields decreased more pronouncedly the narrower the tree spacing had been laid out (see data points by 
Sirohi et al. [18]). The datapoints with crop yields higher inside AF than the corresponding monoculture refer to 
AF systems with spacing between tree rows of 25 m, 40 m, and 48 m, respectively, which is wide spacing compared 
with the majority of the datapoints included in this study. 

LER was significantly positively correlated with the number of trees per hectare (R = 0.561) and with the spacing 
between tree rows (R = 0.26). The former corresponds to a high wood yield of the given agroforestry (AF) systems 
due to a high tree density, while the latter corresponds to high crop yields within the AF systems. LERc was not 
significantly correlated with the number of trees per hectare, but it was positively and significantly correlated with 
the spacing between tree rows (R = 0.5), which underlines that a wider spacing between tree rows impacts crop yields 
to a lesser extent. LERc was significantly and negatively correlated with the tree yield in the given AF systems (R 
= -0.24), which indicates a trade-off between crop yields and tree biomass yield for AF systems with a narrow spacing 
between tree rows.  

In contrast to the experiments listed here, crop yields on average increased in tree windbreak systems, i.e., 
agroforestry (AF) systems with distances between tree rows of 100 m or several hundred meters, which is reflected 
in positive LERc values across crops (Table 7) [16]. Tree yield data of poplars in tree windbreaks versus plantations 
were drawn from our own data in Kyrgyzstan (Table 6). The LER of those systems also indicated an overall increase 
in biomass yields inside AF systems compared to separated monocultures (Table 7).   

 
Table 6. Tree age, DBH, height, volume, biomass, and tree yield of tree windbreaks with 200 m spacing (single row) and corresponding 
plantations in the Jalalabad Region, Kyrgyzstan. Tree windbreaks and plantations consisted of P. nigra, local clone Mirza Terek. 

Tree parameter (Average) Tree wind break Plantation 

Tree age [yr] 10 10 
DBH [cm] 21 17.8 
Height [m] 22.3 19.5 
Tree volume [m³] 0.32 0.2 
Tree biomass [kg] 127 79 
Trees per ha 100 2500 
Biomass [t ha-1] 12.7 198.4 
Yield [t ha-1 yr-1] 1.3 19.8 

 
Table 7. Crop yield increases, LER, and LERc of tree windbreak systems. 

Crop Crop yield increase [%] of crop within tree wind break system, after [16] LER LERc 

Spring wheat 8 1.1 0.08 
Winter wheat 23 1.3 0.23 
Barley 25 1.3 0.25 
Oats 6 1.1 0.06 
Rye 19 1.3 0.19 
Millet 44 1.5 0.44 
Corn 12 1.2 0.12 
Alfalfa 99 2.1 0.99 

 

4. Discussion 
4.1. LER and LERc Values  

Experimental studies of agroforestry (AF) systems with tree species other than poplar or eucalyptus revealed 
LER values larger than one; for example, [19] reported an LER of 1.36 for the AF system of alder and wheat.  

Further studies also underlined that crop yields shrank under agroforestry (AF) systems with a high tree density 
[20], which is due to the shading of the crops. Pardon et al. [21] and Zhao et al. [22] found that crop yields, 
compared to corresponding monocultures, shrank the closer the crop grew to AF trees and the taller those trees 
were. This is compounded by findings from [23] that the photosynthetically active radiation significantly drops 
close to AF trees. Despite the lower crop yields in narrowly spaced AF systems, those systems, in most cases, show 
an increased Land Equivalent Ratio (LER). This can be explained by the high wood yield associated with the high 
tree density, which overcompensates for the loss of crop yields. In other words, the wood biomass yielded from such 
AF systems implies a trade-off in terms of crop yield, which in most cases are food or fodder crops. This trade-off is 
underlined by the mostly negative values of LERc across AF systems and crops, which indicate lower crop yields 
inside AF systems compared to the respective monocultures.  

In the context of tree windbreaks, crop yields were found to be reduced in the neighborhood of windbreaks to a 
distance of 1 x tree height [24], 2 x tree height [25], and 3 x tree height [26], respectively, also due to the shade 
that impacted the given crops. In the case of tree windbreaks with tree row spacing of 100 m and more, crop yields 
do increase on average, while the annual growth of the single agroforestry (AF) trees is also larger than that of trees 
in corresponding plantations. Therefore, tree windbreak systems offer land equivalent ratio (LER) values of larger 
than one, albeit lower than the reviewed alley cropping systems, but without facing the trade-off of sacrificing food 
or fodder crop yields, which is underlined by positive LERc values across all crops (Table 7).  
 

4.2. Discussion of Agroforestry and Sustainable Biomass Sourcing 
This second part of the discussion examines the changes in crop and tree yields of agroforestry (AF) systems 

compared to the respective monocultures in light of the principles for sustainable biomass sourcing [4] that are listed 
in the introduction. 

 Wood biomass sourced from AF systems is a renewable biomass because trees can be regrown after the 
preceding harvest of AF trees. If the AF systems are managed according to so-called good agricultural practices, 



Agriculture and Food Sciences Research, 2025, 12(1): 12-18 

16 
© 2025 by the author; licensee Asian Online Journal Publishing Group 

 

 

which do not degrade soils and water resources, then the production of the wood biomass can be considered 
sustainably managed [5] to adhere to the first principle of BFA [4] for sustainable biomass sourcing.  

According to the results of the agroforestry (AF) experiments listed in this study, food or fodder production is 
compromised when a given crop monoculture is converted into an AF system with narrow spacing between trees, 
high tree density, and hence high yields of woody biomass. This is also reflected in the negative Land Equivalent 
Ratio (LERc) values of those AF systems, as listed in the results section. On the other hand, wood biomass offers an 
additional income to farmers, which may improve food affordability and the social and economic situation of local 
and rural communities, and therefore helps diversify farmers’ income [12]. If the overall social and economic 
situation of the local population is improved, then this second principle would be adhered to. The tree windbreak 
systems (Table 7), however, do adhere to the second principle of BFA [4] for sustainable biomass sourcing, because 
food and fodder production is not compromised, but often even increased compared to a respective monoculture, 
while obtaining an additional benefit from the tree biomass. If plantations of fast-growing trees are planned in areas 
that have not been producing food or fodder, then those plantations can be enriched with an understory crop to form 
AF systems that also adhere to the second principle, because additional food or fodder production is added to a given 
area and its population. 

AF systems must not be established within the area of critical ecosystems in order to avoid directly causing the 
loss of critical ecosystems or habitats of high conservation value. AF systems with negative LERc values, which 
compromise food and fodder production, may lead to land conversion to compensate for the loss of food or fodder 
production, which may indirectly result in the destruction of critical ecosystems or losses of high conservation value 
habitats. Therefore, AF systems with negative LERc values are prone to violate the third principle by BFA [4]. 

AF systems offer a number of benefits to landscape resilience and are resilient to the impacts of climate change 
themselves. The potential of AF systems to improve soil fertility, reduce erosion, improve water quality, and enhance 
the microclimate for crops [10, 11] strengthens landscape resilience and is delivered by AF systems with both high 
and low LER or LERc values alike. AF systems with a high tree density, which tend to deliver reduced crop yields 
compared to respective monocultures, offer a high potential to protect soils from erosion. Gupta et al. [27] showed 
that water erosion of soils was significantly reduced under a poplar AF system with tree spacing of 6.5 m x 4.3 m in 
Punjab, India. Additionally, in New Zealand, poplars and willows have been planted on pastures to form an AF 
system to control water erosion on slopes for the past 60 years [28, 29]. Young eucalyptus plantations (tree age 
between 3 and 7 years) in Brazil reduced soil erosion by more than 50% compared with bare soils on slopes of 20° 
steepness [30]. As a result, the older and larger the eucalyptus tree grew, the lower the soil losses became. 
Furthermore, such systems can improve soil properties, such as infiltration for water, thereby contributing to 
mediating the water cycle and improving water quality [10].  

AF systems with high tree density and reduced crop yields compared to the corresponding crop monocultures 
tend to protect the soil better against erosion. If, in a given region, erosion control on cropland is an overarching 
goal, then introducing AF and careful harvesting of its wood biomass would seem justifiable, as long as the 
affordability of food for the local population is not compromised. Programs to control soil erosion, such as China’s 
so-called Green for Grain Program, incentivized tree planting on mainly marginal cropland prone to erosion (see 
[31]). On the other hand, poplars and eucalyptus trees are substantial water consumers, so newly established AF 
systems with high tree density may over-exploit local water resources and cause water stress in a given landscape, 
as was shown, for instance, for afforestation programs with poplars in northern China [32, 33]. 

AF systems change the microclimate under which the accompanying crops grow through shade (reduced 
radiation), lower temperatures, increased air humidity, and reduced wind speed compared with respective 
monocultures. In particular, tree windbreaks are designed to reduce wind speed and thereby decrease crop water 
consumption, mechanical damage to crops, and wind erosion of cropland soils (Alemu [34]). Thevs et al. [35] 
showed that tree windbreaks of poplars at a spacing of 100 m or more reduced the water consumption of the whole 
AF system compared to the corresponding crop grown as a monoculture. These effects on the microclimate make 
the AF systems themselves more resilient to climate change, specifically increased temperatures, enhanced water 
stress, and extreme weather events, than corresponding crop monocultures, as detailed by Quandt et al. [36]. Thus, 
shading lowers air temperatures and crop water consumption, minimizes soil erosion and soil loss during heavy 
rainfall and/or flood events, and protects crops from strong winds. Reduced wind speeds also correspond with 
lowered crop water consumption and a lower risk of crops suffering from water stress (Weninger et al. [37]). 

The compliance with the principles for sustainable biomass sourcing by BFA [4] AF systems is summarized in 
Table 8. 

 
Table 8. Compliance of AF systems with negative and positive LERc with the principles for sustainable biomass sourcing by BFA [4]. AF 
system refers to AF system.  

Principle AF system with high tree density and 
negative LERc  

AF system with low tree density 
(tree stand breaks, field 
boundaries) and positive LERc. 

Biomass is derived from renewable sources, and 
its production is sustainably managed. 

Adheres to principle. Adheres to principle. 

Biomass sourcing does not adversely impact 
food security and affordability, and it maintains 
or improves social and economic conditions 
along with ecosystem services in producing 
communities. 

Compromises food/fodder production but may 
provide additional income and, hence, improve 
social and economic conditions. Ecosystem 
services are often improved (see explanation in 
the text to principle 4). 

Adheres to principle 

Biomass sourcing does not directly or indirectly 
result in the destruction of critical ecosystems 
or the loss of high conservation value habitats. 

Adheres to the principle, as long as the AF 
system is not established inside the area of 
critical ecosystems. It may result in indirect 
destruction of critical ecosystems or loss of 
high conservation value habitats. 

Adheres to the principle, as long as 
the AF system is not established 
inside the area of critical ecosystems. 

Biomass sourcing contributes to landscape 
resilience and is resilient to the impacts of 
climate change. 

Largely adheres to principles. May cause 
water stress in drylands. 

Adheres to principle. 

 



Agriculture and Food Sciences Research, 2025, 12(1): 12-18 

17 
© 2025 by the author; licensee Asian Online Journal Publishing Group 

 

 

5. Conclusion 
Literature data on poplar and eucalyptus-based agroforestry (AF) systems were reviewed to calculate Land 

Equivalent Ratio (LER) and corrected Land Equivalent Ratio (LERc) values across a range of regions, climates, 
crops, and AF systems, which included alley cropping, plantations with a crop as understory vegetation, field 
boundaries, and tree windbreaks. 

AF systems with narrow spacing and high tree density, i.e., alley cropping, plantations with a crop as understory 
vegetation, and field boundaries, as reviewed in this study, provide high wood biomass yields but often lower crop 
yields than the corresponding crops and trees grown as monocultures. In total, those AF systems deliver more 
biomass than the corresponding crops and trees would deliver when grown as separate monocultures, which results 
in high LER values, as listed above in this study. Yet, the LERc values of most of those AF systems are negative, 
which is a result of the reduced crop yields within those AF systems compared to the corresponding crop 
monocultures. In contrast, tree windbreak systems, in which the spacing between tree lines is much wider than the 
AF systems above, often 100 m and more, show LER > 1 and LERc > 0. This indicates that the tree windbreak 
systems produce more total biomass than the corresponding crops and trees would deliver when grown as 
monocultures and that crop yields do not decrease within those AF systems. 

Given that tree windbreak systems also contribute to soil protection and often improve the microclimate, biomass 
sourced from those agroforestry (AF) systems has a high potential to fulfill the criteria of sustainably sourced 
biomass. Additionally, the AF systems with negative LERc values have the potential to fulfill the criteria of 
sustainably sourced biomass if the overall income and socio-economic situation of the local population is improved 
by, for example, additional income from the woody biomass. If AF systems with high tree density contribute 
substantially to landscape resilience, such as soil protection or regulating the water cycle, they also have the potential 
to fulfill the criteria of sustainably sourced biomass. If landscape resilience is an overarching goal in a given region, 
then AF systems with high tree density should be considered to fulfill the criteria of sustainably sourced biomass. 

 

References 
[1] S. Piotrowski, M. Carus, and R. Essel, "Global bioeconomy in the conflict between biomass supply and demand," Industrial 

Biotechnology, vol. 11, no. 6, pp. 308-315, 2015.  https://doi.org/10.1089/ind.2015.29021.stp 
[2] O. Arodudu, B. Holmatov, and A. Voinov, "Ecological impacts and limits of  biomass use: A critical review," Clean Technologies and 

Environmental Policy, vol. 22, no. 8, pp. 1591-1611, 2020.  https://doi.org/10.1007/s10098-020-01911-1 
[3] UNEP, "Global resources outlook 2024: Bend the trend – pathways to a liveable planet as resource use spikes, International Resource 

Panel: Nairobi," 2024. Retrieved: https://www.resourcepanel.org/reports/global-resources-outlook-2024. 2024. 
[4] BFA, "Methodology for the assessment of  bioplastic feedstocks. WWF," 2022. Retrieved: 

https://www.worldwildlife.org/publications/report-methodology-for-the-assessment-of-bioplastic-feedstocks. 2022. 
[5] RSB, "RSB principles & criteria RSB-STD-01-001. The Roundtable on Sustainable Biomaterials," 2023. Retrieved: https://rsb.org/. 

2023. 
[6] Bonsucro, "Bonsucro production standard version," 2023. Retrieved: https://bonsucro.com/wp-content/uploads/SCH_Bonsucro-

Production-Standard-V5.2-July-2023-ENG.pdf. 2023. 
[7] RTRS, "RTRS standard for responsible soy production. Roundtable on Responsible Soy," 2021. Retrieved: 

https://responsiblesoy.org/wp-content/uploads/2023/03/RTRS-Standard-for-Responsible-Soy-Production-V4.0.pdf. 2021. 
[8] RSPO, "A global certification system for certified sustainable palm oil," 2024. Retrieved: https://rspo.org/as-an-

organisation/certification/. 2024. 
[9] FAO, "Agroforestry," 2024. Retrieved: https://www.fao.org/agroforestry/. 2024. 
[10] S. Jose, "Agroforestry for ecosystem services and environmental benefits: An overview," Agroforestry Systems, vol. 76, pp. 1-10, 2009.  

[11] Α. Pantera, M. Mosquera-Losada, F. Herzog, and M. Den Herder, "Agroforestry and the environment," Agroforestry Systems, vol. 95, 
no. 5, pp. 767-774, 2021.  https://doi.org/10.1007/s10457-021-00640-8 

[12] FAO, "How can fast-growing trees optimize agroforestry benefits," 2024. Retrieved: 
https://openknowledge.fao.org/server/api/core/bitstreams/0cdaeaa6-e4a9-4d59-ae9c-46e50d2e08e9/content. 2024. 

[13] R. Mead and R. Willey, "The concept of  a ‘land equivalent ratio’and advantages in yields from intercropping," Experimental 
agriculture, vol. 16, no. 3, pp. 217-228, 1980.  https://doi.org/10.1017/s0014479700010978 

[14] C. K. Ong and R. M. Kho, A framework for quantifying the various effects of  tree-crop interactions, in C.K. Ong and P. Huxley, Eds., Tree-
crop interactions: a physiological approach. CABI International. 
https://www.cabidigitallibrary.org/doi/pdf/10.1079/9781780645117.0001, 1996. 

[15] FAO (Food and Agriculture Organization of  the United Nations), "Global forest resources assessment 2005: Progress towards 
sustainable forest management," FAO Forestry Paper No. 147. Food and Agriculture Organization of  the United Nations, 2005, 
2005. https://www.fao.org/4/a0400e/a0400e00.htm 

[16] J. Kort, "9. Benefits of  windbreaks to field and forage crops," Agriculture, Ecosystems & Environment, vol. 22, pp. 165-190, 1988.  
https://doi.org/10.1016/0167-8809(88)90017-5 

[17] E. Kimura et al., "Effect of  intercropping hybrid poplar and switchgrass on biomass yield, forage quality, and land use efficiency for 
bioenergy production," Biomass and Bioenergy, vol. 111, pp. 31-38, 2018.  https://doi.org/10.1016/j.biombioe.2018.01.003 

[18] C. Sirohi, K. Bangarwa, R. Dhillon, and K. Bhardwaj, "Performance of  different wheat varieties under poplar (Populus deltoides) 
based agroforestry system," Indian Journal of  Ecology, vol. 43, no. 2, pp. 752-755, 2016.  

[19] L. M. Lehmann et al., "Productivity and economic evaluation of  agroforestry systems for sustainable production of  food and non-
food products," Sustainability, vol. 12, no. 13, p. 5429, 2020.  https://doi.org/10.3390/su12135429 

[20] S. Fang, H. Li, Q. Sun, and L. Chen, "Biomass production and carbon stocks in poplar-crop intercropping systems: A case study in 
Northwestern Jiangsu, China," Agroforestry systems, vol. 79, pp. 213-222, 2010.  https://doi.org/10.1007/s10457-010-9307-x 

[21] P. Pardon et al., "Effects of  temperate agroforestry on yield and quality of  different arable intercrops," Agricultural Systems, vol. 166, 
pp. 135-151, 2018.  https://doi.org/10.1016/j.agsy.2018.08.008  

[22] Y. Zhao et al., "The optimal size of  a Paulownia-crop agroforestry system for maximal economic return in North China Plain," 
Agricultural and Forest Meteorology, vol. 269, pp. 1-9, 2019.  https://doi.org/10.1016/j.agrformet.2019.01.043 

[23] S. Newman, K. Bennett, and Y. Wu, "Performance of  maize, beans and ginger as intercrops in Paulownia plantations in China," 
Agroforestry Systems, vol. 39, pp. 23-30, 1997. https://doi.org/10.1023/A:1005938310106 

[24] R. A. Read, Tree windbreaks for the central great plains. Agricultural Handbook. Washington, DC: U.S.D.A. Forest Service, 1964. 
[25] L. Lyles, J. Tatarko, and J. Dickerson, "Windbreak effects on soil water and wheat yield," Transactions of  the ASAE, vol. 27, no. 1, pp. 

69-0072, 1984.  https://doi.org/10.13031/2013.32737 
[26] B. W. Greb and A. L. Black, "Vegetative barriers and artificial fences for managing snow in the central and northern plains," presented 

at the Snow and Ice in Relation to Wildlife and Recreation, in A.O. Haugen, Ed., Proc. Symp., Iowa State University, Ames, IA, pp. 
96-111, 1971. 

[27] N. Gupta, S. Kukal, and P. Singh, "Soil erodibility in relation to poplar based agroforestry system in North Western India," 
International Journal of  Agriculture and Biology, vol. 8, pp. 859-861, 2006.  https://doi.org/10.1007/s10457-009-9219-9 

[28] I. McIvor, G. Douglas, J. Dymond, G. Eyles, and M. Marden, Pastoral hill slope erosion in New Zealand and the role of  poplar and willow 
trees in its reduction. In D. Godone & S. Stanchi (Eds.), Soil Erosion Issues in Agriculture. Rijeka, Croatia: InTech, 2011. 

https://doi.org/10.1089/ind.2015.29021.stp
https://doi.org/10.1007/s10098-020-01911-1
https://www.resourcepanel.org/reports/global-resources-outlook-2024
https://www.worldwildlife.org/publications/report-methodology-for-the-assessment-of-bioplastic-feedstocks
https://rsb.org/
https://bonsucro.com/wp-content/uploads/SCH_Bonsucro-Production-Standard-V5.2-July-2023-ENG.pdf
https://bonsucro.com/wp-content/uploads/SCH_Bonsucro-Production-Standard-V5.2-July-2023-ENG.pdf
https://responsiblesoy.org/wp-content/uploads/2023/03/RTRS-Standard-for-Responsible-Soy-Production-V4.0.pdf
https://rspo.org/as-an-organisation/certification/
https://rspo.org/as-an-organisation/certification/
https://www.fao.org/agroforestry/
https://doi.org/10.1007/s10457-021-00640-8
https://openknowledge.fao.org/server/api/core/bitstreams/0cdaeaa6-e4a9-4d59-ae9c-46e50d2e08e9/content
https://doi.org/10.1017/s0014479700010978
https://www.cabidigitallibrary.org/doi/pdf/10.1079/9781780645117.0001
https://doi.org/10.1016/0167-8809(88)90017-5
https://doi.org/10.1016/j.biombioe.2018.01.003
https://doi.org/10.3390/su12135429
https://doi.org/10.1007/s10457-010-9307-x
https://doi.org/10.1016/j.agsy.2018.08.008
https://doi.org/10.1016/j.agrformet.2019.01.043
https://doi.org/10.13031/2013.32737
https://doi.org/10.1007/s10457-009-9219-9


Agriculture and Food Sciences Research, 2025, 12(1): 12-18 

18 
© 2025 by the author; licensee Asian Online Journal Publishing Group 

 

 

[29] A. Wilkinson, "Poplars and willows for soil erosion control in New Zealand," Biomass and Bioenergy, vol. 16, no. 4, pp. 263-274, 1999.  
https://doi.org/10.1016/s0961-9534(99)00007-0 

[30] A. H. Oliveira, M. L. N. Silva, N. Curi, J. C. Avanzi, G. Klinke Neto, and E. F. Araújo, "Water erosion in soils under eucalyptus forest 
as affected by development stages and management systems," Ciência e Agrotecnologia, vol. 37, pp. 159-169, 2013.  
https://doi.org/10.1590/s1413-70542013000200007 

[31] C. Lyu and Z. Xu, "Crop production changes and the impact of  Grain for Green program in the Loess Plateau of  China," Journal of  
Arid Land, vol. 12, pp. 18-28, 2020.  https://doi.org/10.1007/s40333-020-0091-9 

[32] S. Cao, L. Chen, and X. Yu, "Impact of  China's Grain for Green Project on the landscape of  vulnerable arid and semi‐arid 
agricultural regions: A case study in Northern Shaanxi Province," Journal of  Applied Ecology, vol. 46, no. 3, pp. 536-543, 2009.  
https://doi.org/10.1111/j.1365-2664.2008.01605.x 

[33] Z. Wang, D. Peng, D. Xu, X. Zhang, and Y. Zhang, "Assessing the water footprint of  afforestation in Inner Mongolia, China," Journal 
of  Arid Environments, vol. 182, p. 104257, 2020.  https://doi.org/10.1016/j.jaridenv.2020.104257 

[34] M. M. Alemu, "Ecological benefits of  trees as windbreaks and shelterbelts," International Journal of  Ecosystems, vol. 6, pp. 10-13, 
2016.  

[35] N. Thevs, A. J. Gombert, E. Strenge, R. Lleshi, K. Aliev, and B. Emileva, "Tree wind breaks in Central Asia and their effects on 
agricultural water consumption," Land, vol. 8, no. 11, p. 167, 2019.  https://doi.org/10.3390/land8110167 

[36] A. Quandt, H. Neufeldt, and K. Gorman, "Climate change adaptation through agroforestry: Opportunities and gaps," Current Opinion 
in Environmental Sustainability, vol. 60, p. 101244, 2023.  https://doi.org/10.1016/j.cosust.2022.101244 

[37] T. Weninger et al., "Ecosystem services of  tree windbreaks in rural landscapes—a systematic review," Environmental Research Letters, 
vol. 16, no. 10, p. 103002, 2021.  https://dx.doi.org/10.1088/1748-9326/ac1d0d 

 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  

Asian Online Journal Publishing Group is not responsible or answerable for any loss, damage or liability, etc. caused in relation to/arising out of the use of the content. 
Any queries should be directed to the corresponding author of the article. 

 

https://doi.org/10.1016/s0961-9534(99)00007-0
https://doi.org/10.1590/s1413-70542013000200007
https://doi.org/10.1007/s40333-020-0091-9
https://doi.org/10.1111/j.1365-2664.2008.01605.x
https://doi.org/10.1016/j.jaridenv.2020.104257
https://doi.org/10.3390/land8110167
https://doi.org/10.1016/j.cosust.2022.101244
https://dx.doi.org/10.1088/1748-9326/ac1d0d

